Dodgy wheel thwarts Mars rover rescue

NASA's attempts to rescue its stuck rover Spirit from a Martian sand trap has hit another snag in the form of a dawdling wheel.

Spirit's right-rear wheel stalled during the agency's third attempt to extract the aging rover from a sandy feature called "Troy" where it has been caught since April.

The space agency was also forced to call short its first round of rescue commands less than 1 second after they began when the rover sensed it was tilting too far for comfort.

NASA began its extrication attempts on November 16 after conducting a lengthy series of trials using a test rover and sandbox on Earth. Doug McCuistion, director of the Mars Exploration program at NASA, has previously stated there's a "high probability" the attempts to free Spirit will not be successful.

The third extrication drive, made on November 21, was halted after the right-rear wheel stalled when its progress fell behind the expected rotation rate, NASA said today. Spirit's wheels completed about 4 meters (13 feet) of commanded spin before the stall terminated the drive. NASA said the effort moved Spirit only 4mm (0.2 inch) forward, 3mm (0.1 inch) to the left and about 3mm (0.1 inch) down.

The aging rover had also experienced stall in its left-middle wheel back in May — but it has since worked normally. Spirit's right-front wheel has been broken since 2006.

Spirit became bogged down in Troy after the rover broke through a hard crust on the Martian surface that was covering bright-toned, slippery sand underneath. NASA's initial attempts to maneuver Spirit to freedom only made the rover sink deeper into the sand.

NASA's plan for today is to run a set of diagnostics to figure out the reason for the right-rear wheel stall. Tests will include a rotor resistance test, a possible steering test, a small backward rotation of the problematic wheel only, and a short forward commanded motion of the rover.

The space agency said it won't resume efforts to free Spirit until Wednesday. ®